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This paper presents experimental results obtained from bench tests on a 1.4 litre, 4-cylinder, dual-fuel spark ignition engine, fitted with a three-way catalytic converter. Performance, fuel consumption and exhaust emissions measurements were recorded under steady state operating conditions from engine builds: (i) with multi-point gasoline liquid fuel injection, and (ii) with single-point vaporised LPG (propane). An after-market LPG conversion kit, incorporating electronic air-fuel ratio control based on exhaust oxygen concentration, was used in the latter case. Emissions were measured before and after the catalytic converter and catalyst conversion efficiency trends are presented for each fuel.

The experimental data is also compared with predictions from a thermodynamic cycle simulation and emissions prediction model which was developed with a view to gaining an improved understanding of the observed experimental trends.

CONVERSION OF light duty vehicle spark ignition engines to operation on liquefied petroleum gas (LPG) presents some difficulties in the areas of electronic engine management and control of exhaust emissions. Suppliers of after-market LPG conversion kits are faced with a very large variety of vehicle types and engine options where the size of the market for any specific combination may be small. Development of complete alternative engine management systems with fully optimised spark timing maps is not feasible and it is common practice to supply an additional electronic unit which controls fuelling only, typically using a feedback signal from an exhaust oxygen sensor. Some results [1, 2] have published from emissions oriented studies on such systems.